March 24 (UPI) -- The guided missile cruiser USS Monterey visited Romania this week, and participated in a NATO exercise in the Black Sea that saw Russia deploy six submarines in response to the international presence.
The USS Monterey, part of the USS Dwight D. Eisenhower Carrier Strike Group, conducted a port call in Romania on Monday and Tuesday after Sea Shield 2021, an annual naval exercise led by Romania, on March 19 and 20, the Navy said Wednesday.
Eighteen NATO warships, 10 aircraft and 2,400 troops were involved in the annual exercise, meant to enhance interoperability and cooperation between NATO naval forces.
The USS Monterey, USS Thomas Hudner and P-8 surveillance aircraft of the strike group's Patrol Squadron 46 participated in the exercise.
The exercise also included naval representatives of Albania, Bulgaria, Croatia, France, Greece, Italy, Japan, the Netherlands, Poland, Spain, Standing NATO Maritime Group Two, Turkey, Britain, and Ukraine.
On Wednesday, the USS Monterey concluded its Black Sea operations and transited to the Mediterranean Sea.
"Our operations in the Black Sea demonstrate our commitment to NATO partners and supported the provision of stability in the maritime environment through reassuring presence of an active naval force to deter destabilizing activity," Capt. Joseph A. Baggett, commanding officer of the Monterey, said in a press release.
In apparent response to the exercise, all Russian submarines in Black Sea ports were deployed on Friday.
Capt. Anatoly Varachkin, senior officer of Russia's Black Sea Fleet submarine brigade, said in a press release that all submarines under his command are at sea.
"This is an unprecedented case, which is not found either in the fleets of the Russian Federation or in the fleets of foreign states," Varachkin said.
Russia views NATO's eastward expansion as a national security risk, and NATO members regard recent missile deployments in Kaliningrad, a Russian territorial exclave between Poland and Lithuania, with wariness.
Both sides see the Black Sea, bordered by Russia and NATO members Turkey, Ukraine, Georgia, Bulgaria and Romania as a critical waterway for European maritime commerce and stability in Europe.
Earlier in March, the USS Monterey conducted a joint maritime security patrol with the Israeli Sa'ar 4.5 ships in the Eastern Mediterranean Sea.